を以て【をもって】

をもって以て is a formal "with": it marks the means by which something is done, or the point in time at which something ends or takes effect. It goes straight after a noun. Modern writing usually spells it in kana, をもって, and it belongs to announcements, ceremonies, business letters and official documents.

The end point

This is the use you see most, on shop doors and notices. The date named is the last day: the thing stops at the close of it.

をもちまして is the polite form, heard at the end of ceremonies and in announcements. In ordinary speech, で does the same job: きょう今日でへいてん閉店です.

Means – "with", "by"

For the means, を以て replaces で in formal writing. It goes with weighty nouns: sincerity, all your strength, a written document, a majority vote.

• × 箸を以てご飯を食べる → 箸でご飯を食べる

The thing that earns a reward or a penalty can also take を以て: そのこうせき功績をもって以てひょうしょう表彰された, "he was honoured for those achievements".